1. Field of the Invention
This invention relates generally to electrochemical cells and, more particularly, this invention relates to power modules of the electrochemical type.
2. Description of the Prior Art
Electrochemical cells utilizing consumable, reactive metal anodes are well known. Multi-cell assemblies of such electrochemical cells or batteries to which this invention relates normally include a plurality of anodes and cathodes arranged in spaced relation within an overall case. The multi-cell assemblies have anodes and cathodes arranged in stacked relation within the overall case and electrolyte is flowed across the faces of adjacent anodes and cathodes.
In one conventional form of electrochemical power module for providing electrical power, the anodes and cathodes are provided on opposite sides of bipolar plates to define bipolar electrodes connected in series between a pair of spaced end plates which define the ends of the case. An electrolyte is flowed across the spaced faces of adjacent anodes and cathodes. Typically, each anode comprises an alkali metal, such as lithium, in elemental, compound, complex, amalgam or mixture form, in conjunction with a cathode typically of a suitable metal such as iron or silver oxide, and an aqueous or non-aqueous electrolyte The electrolyte normally comprises an aqueous solution of lithium hydroxide
Such cells are described in detail in numerous patents and publications, including U.S. Pat. Nos. 3,791,871 (Rowley); 3,976,509 (Tsai et al); 4,007,057 (Littauer et al); and 4,188,462 (Klootwyk). Such electrochemical cells or batteries provide significant power output, but have the disadvantage of relatively high weight and cost. Therefore, such cells may not be desirable for use in aeronautical applications, for instance.
Another conventional form of electrochemical cell for providing electrical power utilizes a lithium anode and an air cathode. An example of an electrochemical cell having an air cathode is shown in U.S. Pat. No. 4,528,249 (Galbraith). Such cells do not provide the power output of conventional metal cathode cells, but they are of relatively low weight and cost.
In either form of electrochemical cell, intercell resistance losses are of concern. Such losses are a source of lost power. In either form of electrochemical cell, the anode usually is the consumable electrode. As the lithium or like material anode is consumed, the resistance paths are increased. Consequently, various attempts have been made to maintain constant electrode spacing as the anode is consumed.
For instance, in U.S. Pat. Nos. 4,189,528 (Klootwyk) and 4,200,685 (Klootwyk et al), power module assemblies are shown in the form of electrochemical batteries which include a plurality of anode-cathode units arranged in stacked relation within a housing. As the anodes are consumed, the stack is compressed by means of a pressure device including an expandable chamber at one end of the stack for transmitting pressure to the stack by introducing fluid under pressure into the expansion chamber. In U.S. Pat. No. 4,188,462 (Klootwyk), each cell in the bipolar module is a single unit which includes a pressure device in the form of an expansion bag for engaging the anode to accommodate anode erosion.
While the use of pressure devices such as expansion chambers, in the form of bellows or bags of the prior art, have proven effective to some degree in reducing shunt losses, certain problems still have not been met. For instance, when expansion chambers are utilized at one end of a stack of cells in an overall case, the problem of friction or drag on the individual cells causes uneven forces and sometimes jamming of the cells within the overall case. In addition, as the individual cells are moved to one end of the case during anode consumption, the center of gravity and balance of the overall cell changes. Even when individual expansion chambers are used for each individual cell, compensation is not made for uneven consumption of the respective anode itself. In other words, in order to maintain true spacing between the anode and the cathode, compensation must be made for uneven anode erosion which results in "cocking" of the anode. Such problems have not been adequately addressed by the prior art.
Furthermore, the use of such expansion chambers have been primarily applied to metal anode and cathode arrays, and not to air cathode electrochemical cells. With air cathode cells, a sealing problem always is encountered because of the use of different fluids, i.e. air and electrolyte.
Another problem with electrochemical cells involves providing adequate protection around the edges or perimeter of the consumable anode so that the anode does not wear unevenly about the perimeter. If the perimeter is not adequately protected, due to the well-known reaction of the anodic metal with the electrolyte, the anode wears unevenly about the perimeter, resulting in significantly decreased battery power and energy output, while proportionately increasing the cells heat and hydrogen gas output rate. This problem is described in U.S. Pat. No. 4,564,570 (GORDON).
A further problem found in electrochemical cells of the type herein described resides in the fact that as the anode plates are consumed, they tend to become unstable and to break apart. This problem is described in U.S. Pat. No. 4,317,863 (STRUTHERS).
This invention is directed to solving one or more of the above problems by providing a new and improved power module for accommodating anode consumption and eliminating intercell resistance losses in either a metal cathode or air cathode form of electrochemical cell.